This proposal investigates a powerful form of implicit visual learning - contextual cueing (Chun & Jiang, 1998). Contextual cueing reflects the influence of attention by implicitly-learned visual context. In this task, subjects search for a "T" among "L"s. When the spatial layout formed by all items repeats occasionally, search is faster among the repeated displays than among the new ones, suggesting that the repeated context "cues" attention to the target position. Contextual cueing is (1) fast, acquired after 4-5 repetitions, (2) long-lasting, persisting for at least a week, and (3) implicit, requiring no conscious effort to learn. This proposal has four specific Aims. 1. Is contextual cueing automatic or attention-dependent? To find out, subjects will be asked to attend to a subset of items and ignore the others and learning of the ignored repetition will be measured. 2. Do subjects learn the global spatial layout formed by all items or do they learn the individual item locations? To this end, we will measure whether contextual cueing transfers to displays whose global context or local context is selectively disrupted. 3. What is the extent of individual variabilities in contextual cueing and what is the source of such variation? We will measure the correlation between an individual's cueing effect and other cognitive abilities, such as digit-span, visual short-term memory capacity, and central executive function. 4. Do common brain regions underlie encoding display repetitions and learning of a consistent association? Here, we will use fMRI to measure brain regions important for repetition processing and those for associative learning. This proposal has direct health implications because unlike explicit learning and memory, implicit learning is largely preserved in many patient groups, in people with low IQ, and in small children and older adults. Contextual cueing is a powerful form of implicit learning. Understanding its cognitive and neural mechanisms is the first step toward understanding this ability in normal adults as well as in those whose explicit learning and memory mechanisms are impaired.